The present invention relates to a tandem rolling mill facility and a rolling method using the tandem rolling mill facility, and particularly, to a tandem rolling mill facility comprising a rolling mill line in which rolling mills are arranged in a plurality of stands aligned in a pass direction of a rolled material, each of the rolling mills having working rolls arranged so as to be offset with respect to rolls placed on and under the working rolls, and to a rolling method using the tandem rolling mill facility.
In general, a tandem rolling mill facility comprises a rolling mill line composed of a plurality of rolling mills, each of which has working rolls and supporting rolls placed on and under the working rolls, aligned in a pass direction of rolled material, and rolling work is performed using the working rolls as the driving roll while a tension is being added to a rolled material wound in a pay-off reel placed in an inlet side of the first stand and in a tension reel in an outlet side of the final stand. Further, there is a tandem rolling mill facility which has bridle rolls arranged in the inlet side or the outlet side of a rolling mill line composed of a plurality of rolling mills in order to add a desired tension to a rolled material, and the tandem rolling mill facility is installed in a continuous line. In the tandem rolling mill facilities described above, the working rolls are generally arranged with an offset so that the center axes of the working rolls are slightly displaced to the center axes of the supporting rolls placed on and under the working rolls in order to obtain a stable rolling condition, as described in Japanese Patent Publication No. 60-16283.
That is, in a case where there is a difference in tensions added to an inlet side and an outlet side of a rolled material, bearing boxes of the working rolls are always pushed toward a side of larger tension, the inlet side or the outlet side, by arranging the center axes of the working rolls so as to be offset toward the side of the larger tension with respect to the center axes of the supporting rolls placed on and under the working rolls, and consequently stable rolling can be attained. For example, in a conventional high-speed tandem rolling mill facility, in the first stand a tension in the outlet side is extremely large compared to a tension in the inlet side, and in the final stand a tension in the inlet side is extremely large compared to a tension in the outlet side. In such a facility, the center axes of the working rolls in the rolling mill placed at the first stand are arranged so as to be offset toward the outlet side of the rolled material with respect to the center axes of the supporting rolls arranged on and under the working rolls, and the center axes of the working rolls in the rolling mill placed at the final stand are arranged so as to be offset toward the inlet side of the rolled material to the center axes of the supporting rolls arranged on and under the working rolls. By doing so, a stable rolling condition can be obtained.
In recent years, users"" requirements for properties of plate materials manufactured by rolling of various kinds of materials have become increasingly severe, and it is required to control the plate thickness in high accuracy. Further, there are very high needs to use small diameter working rolls because of requirements to increase a rolling-down ratio at rolling and to add higher gloss. However, there is a problem in that the working rolls are apt to be horizontally deflected to deteriorate the control characteristic of the plate shape if small diameter working rolls are used in the conventional tandem rolling mill facility.
That is, offset-arranging the working rolls as described above is producing a horizontal force (an offset force) in the working rolls, and a stable rolling condition can be obtained by adding the offset force in the same direction as the direction toward the side of the larger tensile. However, the working rolls are apt to be horizontally deflected to deteriorate the control characteristic of the plate shape because the horizontal force of the sum of the difference of tension and the offset force acts on the working rolls. When the horizontal force is constant, the tendency described above becomes larger as the diameter of the working rolls is smaller.
When the working rolls are arranged so as to be offset toward a side opposite to the side of larger tensile force of the rolled material with respect to the top and the bottom supporting rolls, the horizontal force acting on the working rolls becomes smaller because the difference of tensile force and the offset force are compensated with each other. However, when the working rolls are arranged so as to be offset as described above, there is a possibility that the direction of the horizontal load of the sum of the difference of tensile force and the offset force may be reversed between the inlet direction and the outlet direction by change in the rolling condition (that is, by the magnitude of the rolling load) because the magnitude of the offset force is determined by the rolling load.
Particularly in the final stand of the rolling mill line, the horizontal unbalance state due to the difference between the offset force and the tension is largely changed by rapid decrease of the tensile force in the outlet side caused by cutting of the rolled material using a shear machine placed behind (the outlet side of) the final stand. That is, the method of changing the offset arrangement in a direction so as to compensate the difference of tension with the offset force is not desirable for realizing stable rolling.
In the tandem rolling mill facility using small diameter working rolls which are apt to be deflected as described above, in order to reduce the horizontal force acting on the working rolls to suppress the horizontal deflection in taking the plate shape control characteristic into consideration, the center axes of the working rolls are arranged so as to be offset toward a side opposite to the side of larger tension with respect to the axes of the supporting rolls on and under the working rolls. However, in that case, it is difficult to realize stable tandem rolling because fluctuation of the working rolls may occur depending on change in the rolling condition, as described above. Further, there are some cases where an abnormal phenomenon such as occurrence of vibration sound during rolling or occurrence of periodical variation of plate thickness, called as chattering, in the rolled material.
A first object of the present invention is to provide a tandem rolling mill facility which can perform rolling excellent in the plate shape control characteristic using small diameter working rolls, and to provide a rolling method using the tandem rolling mill facility.
A second object of the present invention is to provide a tandem rolling mill facility which can compromise the conflicting characteristics when rolling is performed in a tandem rolling mill facility using the small diameter working rolls, and can realize rolling excellent in the plate shape control characteristic, and can attain a stable rolling condition.
(1) In order to attain the first object described above, a tandem rolling mill facility in accordance with the present invention comprises a rolling mill line aligning a plurality of rolling mills in a pass direction of a rolled material, the rolling mill having top and bottom working rolls and top and bottom supporting rolls arranged on and under the working rolls, wherein at least one rolling mill among the plurality of rolling mills is a working roll offset rolling mill in which the top and the bottom working rolls are used as driving rolls, and axes of the top and the bottom working rolls are arranged so as to be offset to a side opposite to a side of larger tension acting on the rolled material with respect to axes of the top and the bottom supporting rolls.
By arranging the axes of the top and the bottom working rolls so as to be offset to the side opposite to the side of larger tension acting on the rolled material with respect to the axes of the top and the bottom supporting rolls, a horizontal force acting on the working rolls can be reduced. As the result, the deflection of the working rolls can be decreased, and accordingly rolling excellent in plate shape control characteristic can be performed using small diameter working rolls.
(2) In the above item (1), it is preferable that the working roll offset rolling mill is arranged at least in the final stand of the rolling mill line.
Thereby, rolling excellent in plate shape control characteristic can be performed using small diameter working rolls in the final stand.
(3) Further, in order to attain the second object described above, in the tandem rolling mill facility described in the above item (1) or (2), the working roll offset rolling mill comprises an actuator for pushing bearing boxes of the top and the bottom working rolls against fixed portions.
By providing the actuator for pushing the top and the bottom working rolls as described above, even if a direction of a horizontal force of the sum of a difference of tensions and an offset force is reversed between the inlet side and the outlet side due to change in the rolling condition particularly in the final stand, it is possible to prevent the working roll bearing box from moving. Therefore, rolling excellent in plate shape control characteristic can be performed using small diameter working rolls, as described above, and a stable rolling condition can be obtained.
(4) In the above item (3), it is preferable that the actuator is arranged so as to push the bearing boxes of the top and the bottom working rolls to the same side as the offset direction of the top and the bottom working rolls.
Thereby, during normal rolling, the working roll bearing boxes can be stably held with a weak force because the horizontal force acting on the working rolls is a force toward the outlet side (the offset direction of the working rolls) in most cases particularly in the rolling mill in the final stand.
(5) In the above items (1) to (4), it is preferable that the top and the bottom working rolls are comparatively small diameter working rolls having B/L smaller than 0.26, where B is a diameter of the top and the bottom working rolls and L is a plate width of the rolled material.
By applying the present invention to the comparatively small diameter working rolls having B/L smaller than 0.26, the maximum horizontal deflection of the working roll can be substantially reduced, and accordingly rolling excellent in plate shape control characteristic can be performed using small diameter working rolls.
(6) Further, in order to attain the second object described above, in the tandem rolling mill facility described in the above item (1), all of the plurality of rolling mills are the working roll offset rolling mills, and at least the rolling mill placed in the final stand of the rolling mill line comprises an actuator for pushing bearing boxes of the top and the bottom working rolls against fixed portions.
Thereby, the horizontal force acting on the working rolls in all the rolling mills can be decreased, and the horizontal deflection of the working rolls can be decreased, and accordingly rolling excellent in plate shape control characteristic can be performed using small diameter working rolls. Further, even if a direction of a horizontal force is reversed in the final stand, it is possible to prevent the working roll bearing box from moving. Therefore, a stable rolling condition can be obtained.
(7) Further, in order to attain the first object described above, a tandem rolling mill facility in accordance with the present invention comprises a rolling mill line aligning a plurality of rolling mills in a pass direction of a rolled material, the rolling mill having top and bottom working rolls and top and bottom supporting rolls arranged on and under the working rolls, wherein at least one rolling mill placed in the final stand among the plurality of rolling mills is a rolling mill in which the top and the bottom working rolls are used as driving rolls, and axes of the top and the bottom working rolls are arranged so as to be offset to an outlet side of the rolled material with respect to axes of the top and the bottom of supporting rolls, and the other rolling mills are rolling mills in which the top and the bottom working rolls are used as driving rolls, and axes of the top and the bottom working rolls are arranged so as to be offset to an inlet side of the rolled material with respect to axes of the top and the bottom supporting rolls.
(8) Further, in order to attain the second object described above, in the tandem rolling mill facility of the item (7), at least the one rolling mill placed in the final stand comprises an actuator for pushing bearing boxes of the top and the bottom working rolls against fixed portions.
Thereby, even if a direction of a horizontal force is reversed in the final stand, it is possible to prevent the working roll bearing box from moving. Therefore, a stable rolling condition can be obtained.
(9) Further, in order to attain the first object described above, a tandem rolling mill facility in accordance with the present invention comprises a plurality of rolling mills each having a pair of top and bottom working rolls, and a pair of supporting rolls, wherein an offset means for offsetting the working rolls toward an outlet side of a rolled material with respect to the supporting rolls is provided at least the rolling mill in a final stand.
Thereby, the deflection of the working rolls can be decreased, as described above, and accordingly rolling excellent in plate shape control characteristic can be performed using small diameter working rolls.
(10) Further, in order to attain the first object described above, a tandem rolling mill facility in accordance with the present invention comprises a plurality of rolling mills each having a pair of top and bottom working rolls, and a pair of supporting rolls, wherein an offset means for offsetting the working rolls toward an outlet side of a rolled material with respect to the supporting rolls is provided at least the rolling mill in a final stand, and an offset direction by said offset means is a direction opposite to a side of larger tension acting on the rolled material.
Thereby, the deflection of the working rolls can be decreased, as described above, and accordingly rolling excellent in plate shape control characteristic can be performed using small diameter working rolls.
(11) Further, in order to attain the first object described above, a rolling method in accordance with the present invention uses a tandem rolling mill facility which comprises a plurality of rolling mills each having a pair of top and bottom working rolls, and a pair of supporting rolls, wherein an offset means for offsetting the working rolls toward an outlet side of a rolled material with respect to the supporting rolls is provided at least the rolling mill in a final stand, and rolling is performed while the working rolls are being offsetting to a direction opposite to a side of larger tension acting on the rolled material by the offset means.
Thereby, the deflection of the working rolls can be decreased, as described above, and accordingly rolling excellent in plate shape control characteristic can be performed using small diameter working rolls.